The present invention relates to a semiconductor device which allows packaging of high density for protecting an integrated circuit formed on a semiconductor chip and ensuring electrical connection between the integrated circuit and an external device in its chip shape, and relates to a method for fabricating the same.
In recent years, as electrical equipment becomes more downsized and more sophisticated in functionality, semiconductor devices (semiconductor packages) have been requested to provide multiple terminals resulting from miniaturization and greater packing density of the packages. To respond this request, various types of chip scale packages (CSPs) have been developed as small-size packages having multiple terminals.
In particular, a wafer-level CSP (WL-CSP) has recently received attention as a technique capable of providing the ultimate small-size package having a size similar to that of a bare chip. The WL-CSP is formed by applying an insulating resin film on the entire surface of a semiconductor wafer on which a plurality of integrated circuits are provided, forming on the applied film interconnects for electrically connecting pad electrodes of the integrated circuits to external terminals such as bumps through contact holes, and dividing the semiconductor wafer into chip-size parts in the final process step.
Moreover, an enhanced semiconductor package was announced in which inductors, conventionally provided as separate components from the semiconductor chip, that is, provided as so-called external components, were formed on an insulating resin film of a WL-CSP semiconductor device by the use of materials constituting interconnects of the device to external terminals. The WL-CSP semiconductor device having inductors is also expected as an ultrasmall semiconductor package applicable to applications utilizing a frequency of hundreds of megahertzes (MHz) to several gigahertzes (GHz), such as potable devices and wireless LAN devices.
Hereinafter, a conventional WL-CSP semiconductor device having inductors formed on an insulating resin film covering an integrated circuit will be described with reference to the accompanying drawings.
FIG. 7 is a perspective view showing the conventional WL-CSP semiconductor device, in which an outer insulating film is partly broken away to expose inductors and some of interconnects.
As shown in FIG. 7, a first insulating resin film 102 having a thickness of about 4 μm to 6 μm is formed, through a passivation film, on the main surface of a semiconductor chip 101 with an integrated circuit formed on the main surface. In the first insulating resin film 102, a plurality of contact holes 103 are formed to expose pad electrodes (not shown) of the integrated circuit.
A plurality of lands 104 of substantially flat-circular shape are formed on the first insulating resin film 102. On the film 102, interconnects 105 are also formed of which one end is connected to the corresponding contact hole 103 and of which the other end is connected to the corresponding land 104. Regions of the first insulating resin film 102 provided with the lands 104 relatively sparsely are formed with an inductor 106 of which both terminals are connected to the pad electrodes through the contact holes 103, respectively. In this structure, the land 104, interconnect 105 and inductor 106 are patterned by copper (Cu) plating using a resist pattern as a mask.
On the first insulating resin film 102, a second insulating resin film 107 is formed which covers the interconnects 105 and the inductors 106 and which has a plurality of openings 107a exposing the lands 104. Over each of the openings 107a, an external terminal 108 of a soldering paste material is formed by printing.
The characteristic of an inductor is generally expressed by a Q value. The Q value is obtained by dividing a value of an energy input supplied to an inductor by a value of an energy loss caused by the inductor. Thus, the higher the Q value is, the smaller the energy loss of the inductor becomes.
In the conventional WL-CSP semiconductor device described above, the loss energy of the inductor 106 is the total of a heat loss caused by a resistance component of the inductor 106, a dielectric loss caused in the first and second insulating resin films 102 and 107 or the like, and a loss caused by signal leakage from the inductor 106 into the semiconductor chip 101 through the first insulating resin film 102 (referred hereinafter to as a leakage loss).
The heat loss is substantially determined by the size and the material of the inductor 106, and the dielectric loss is substantially determined by the material of the first and second insulating resin films 102 and 107. To reduce the leakage loss, the first insulating resin film 102 needs only to be thick. Herein, FIG. 8 shows an exemplary result of calculation on the frequency dependence of the Q value of the inductor 106 using the thickness of the first insulting resin film 102 as a parameter. As shown in FIG. 8, it is clear that as the thickness of the first insulating resin film 102 is increased from 4 μm to 10 μm, the Q value thereof increases.
However, the first insulating resin film 102 of the above conventional WL-CSP semiconductor device has the upper limit in thickness of about 4 μm to 6 μm. The reason for this is that the conventional WL-CSP semiconductor device uses a photosensitive resin material for the first insulating resin film 102, and therefore the first insulating resin film 102 has a limitation of the thickness according to the resolution of light exposure in forming the contact hole 103 in the first insulating resin film 102. This thickness limitation makes it impossible to thicken the first insulating film 102 to such a thickness that a leakage loss in the inductor 106 is reduced sufficiently. Therefore, high-frequency signals leak from the inductor 106 into the semiconductor chip 101 through the first insulating resin film 102. The leakage loss in the inductor 106 thus caused is too great to ignore, so that application of the WL-CSP semiconductor device shown in FIG. 7 to a high-frequency device causes the problem of a significant degradation of the high-frequency properties thereof.